The opportunity afforded by improving the thermal efficiency of internal combustion engines (ICE) (commonly 28% for gasoline, 34% for diesel engines) is well understood, however long-standing research and development efforts have not produced marked technical and/or market impacts. Turbo-charging and ceramic insulation of combustion chamber components have made the most significant impact, however, cost and the extent of efficiency improvement (−10%), has not led to a significant reduced fuel consumption on a functional work unit basis, and accordingly not impacted the per capita basis. Exhaust gas turbines with mechanically-connected generators have been presented as alternative, however, cost and efficiency have similarly pre-empted commercialization. Thermal-to-Electric devices and systems have also been presented to capture the waste stream energy, however, the device efficiencies for prior thermoelectric and thermionic cases, have been very low (<10%), limiting the use to lesser power applications. Efficient use of prior devices were also limited to very high temperatures, typically requiring >700° C. The design of the thermal transfer system encapsulating the thermoelectric or thermionic devices have lacked adequate transfer surface and residence time, resulting in reduced energy extraction from the bulk stream.
In the case of transportation vehicles, having proliferated a high-mass (high load) basis contributes to the magnitude of the loss, and increases the magnitude and cost of thermal recovery options. Higher fuel prices have inspired the market for vehicles with hybrid drivetrains (ICE assisted by a generator (s) with energy storage system, yet the approximate 70% wasting of exhaust energy continues in these systems as well.
U.S. Pat. No. 4,148,192 describes a “parallel” internal combustion electric hybrid powerplant having thermoelectric devices positioned in such manner as to receive heat energy from the engine exhaust and deliver electrical energy to the system's battery. The thermal conversion elements are attached to the exterior surfaces of the exhaust pipe and the cylinder walls.
U.S. Pat. No. 4,489,242 Discusses the use of a stored energy system to provide the necessary energy for operation of a vehicle's accessories, and includes a suggestion for an exhaust-driven thermoelectric unit, amongst a multitude of options (without detail sufficient to build or determine viability of such an approach).
Laid-open application US2006/0000651 describes the same invention of the former 4,148,192
U.S. Pat. No. 5,857,336 Describes an exhaust-driven turbo-assisted positive displacement engine for a hybrid electric vehicle, and having a second exhaust passage with another turbine which mechanical turns a (mechanical) generator to recover additional energy when the waste-gate bypasses the first turbo.
U.S. Pat. No. 7,100,369 describes a thermoelectric device system extracting heat from the exhaust stream of an engine having a primary and secondary exhaust passages and control valves operated based upon engine load for optimization.
U.S. Pat. No. 6,605,773 presents a thermoelectric generator for a fuel-cell power plant of a vehicle, having a thermally-activated regulator controlling the heat source (fuel cell) and/or the cooling medium to the generator, thereby eliminating the cost and complexity of a DC-DC converter.
U.S. Pat. No. 7,068,017 describes a source regulation (impedance transformation) electrical system used to increase the efficiency of power transfer from a direct energy source (one example, of many, and not described with sufficient detail as to allow construction or viability) being a thermoelectric or thermionic device) to the load.
U.S. Pat. No. 7,111,465 presents improved thermoelectric generator design by thermal isolation of thermoelectric devices in an array. Laid-open application US200510204762 presents a thermoelectric generation system interfaced to the combustion exhaust stream via a heatpump with liquid circulation system having an endothermic reaction.
Laid-open application US200510204733 presents the invention of the former US2005/0204762 with the introduction of the catalytic treatment of the exhaust, and options for integration and optimization with the thermoelectric system.
Laid-open application US200510074645 describes a thermoelectric generating system capturing heat from a solid oxide fuel cell, the generating system having a vacuum enclosure surrounding the thermoelectric devices (for thermal isolation).
The opportunity presented by thermoelectric capture of waste energy is best extracted when applied to an efficient vehicle and hybrid drive system. A strong relationship has been established between vehicle weight and fuel efficiency (EPA data: 1 gallon/100 miles/900 pounds), implying that vehicle weight, and the hybrid drive system itself, must be weight conscious to offer marked improvement (FIG. 8) (present invention performance marked as “ES 1”. Not surprisingly, today's hybrids offer only minor improvement in fuel efficiency over non-hybrids, as they leverage the same heavyweight automobile platform with the additional weight of hybrid components. In particular battery-based storage systems are comparatively low in power density (200 to 400 Wkg for today's advanced types), yet high in energy density (200 W-hrkg). In addressing the power demands and overcoming poor charge and discharge efficiencies (70-90% dependent upon technology and state-of-charge (SOC)), battery mass becomes a significant weight contributor. Excessive energy storage has led to hybrid designed for long cycle times (lengthy discharge and charge times).
The inability of batteries to charge and discharge at high rates and high efficiencies, has been an impetus to augment the storage with higher power density medium, e.g. ultracapacitors (˜6000 W/kg) for the high rate conditions. Unfortunately the combination of batteries and ultracapacitors brings about other limitations, as well as added costs, complexity and reduced reliability. For a series combination of batteries and ultracapacitors, the battery limits the current rate, so little improvement in charge/discharge rate occurs. When used in parallel, the ultracapacitors, whose characteristic voltage change is stronger than the battery for a given charge/discharge rate, the battery limits the capacity use. A pure ultracapacitor storage solution was not envisioned for automobile application, as ultracapacitors are too low in energy storage (<10 W-hr/kg) to accommodate the mass-driven requirements of the current automobile platform.
Others have identified approaches with switched banks of UC's, or in combination with batteries, to avert the extreme voltage reduction that would be experienced by continuing to draw from a single UC. However, this methodology results in significant underutilization of the capability of the UCS (typically less than 50% as voltage input variations are limited to 2:1 for many devices). The additions of banks (either battery or UC) bring increased switching components/complexity, efficiency loss, increased weight (reducing vehicle efficiency) and cost.
U.S. Pat. No. 6,265,851 describes an electric vehicle power system for a semiconductor wafer handling application, having ultracapacitors and batteries as parallel sources connected to a source-selecting switch and having said switch direct its output only to a DC-DC converter which serves the motor load, however, this incurs the converter losses when no conversion is necessary.
Laid open US Pat App. US 2004/0100149 describes topologies for multiple energy sources, including UCs, and accommodates reverse power flow from the utility being driven (case of regenerative braking for a transportation vehicle). In the described topologies, all power is continuously directed through a power converter module, with inherent losses and limitations per device sizing.
U.S. Pat. No. 7,004,273 discusses a bank of ultracapacitors directly bussed to an engine-driven generator with a control management unit bringing the engine on and off to maintain the state-of-charge of the ultracapacitors. This approach does not address the inefficient ultracapacitor capacity utilization issue, resulting in extensive burden/cycling of the engine and/or significant oversizing of the ultracapacitor bank.
U.S. Pat. No. 7,109,686 describes the use of braking resistor and switch structure to assist in charging and discharging an ultracapacitor bank and to protect the ultracapacitor from excessive pre-charge current. A DC-DC converter is referenced as expensive, and its use is referenced only as an alternative method to pre-charge the ultracapacitor bank. While low in cost the use of the braking resistor diverts energy, thereby wasting said energy.
A solution which could extract more of an ultracapacitor's capacity would greatly assist in reducing wasted capacity and enable an all-ultracapacitor storage solution for a lightweight vehicle. Augmentation with thermal-to-electric recovery of waste heat furthers this potential.